ArsDigita Keepalive is a system that monitors your web services at regular, short intervals, and takes
action to resolve problems found. If Keepalive fails to reach a page, depending on how many consecutive
previous failures it has seen and the configuration parameters, it will take one of the following actions:

nothing except decrement a counter

send email to a previously defined group of addresses

execute a shell command, presumably one that restarts the stuck service

For more information, visit http://www.arsdigita.com/free-tools/keepalive.html